Without limiting the scope of the invention, its background is described in connection with lightweight polymer subsonic ammunition casing and more specifically to a lightweight polymer subsonic ammunition casing having a propellant insert positioned in the propellant chamber to reduce the internal volume of the propellant chamber.
Generally, there are two types of ammunition: supersonic ammunition, which fires projectiles with velocities exceeding the speed of sound; and subsonic ammunition, which fires projectiles with velocities less than that of the speed of sound and generally in the range of 1,000-1,100 feet per second (fps), most commonly given at 1,086 fps at standard atmospheric conditions. Traditional methods of making subsonic ammunition reduce the propellant charge (and in turn increasing the empty volume left vacant by the reduced propellant charge) in the shell until the velocity is adequately reduced.
Unfortunately, this empty volume can cause numerous problems including inhibition of proper propellant burn, inconsistent propellant positioning, reduced accuracy and propellant detonation caused by extremely high propellant burn rates. For example, since the propellant is free to move in the large empty volume, shooting downward with the propellant charge away from the primer gives different velocity results than when shooting upwards with the propellant charge close to the primer. Finally, usage of subsonic ammunition, and its attending lower combustion pressures, frequently results in the inability to efficiently cycle semi-automatic or fully automatic weapons where the propellant charge must produce sufficient gas pressure and/or volume to accelerate the projectile and to cycle the firing mechanism. With a reduced quantity of propellant, subsonic ammunition generally fails to produce sufficient pressure to properly cycle the firing mechanism. The art has provided numerous attempts to cure these problems, e.g., the introduction of inert fillers, expandable inner sleeves that occupy the empty space between the propellant and the projectile, insertion of flexible tubing, foamed inserts, stepped down stages in the discharge end of cartridge casings, or complicated three and more component cartridges with rupturable walls and other complicated features. Another approach has been to use standard cartridges in combination with non-standard propellants. However, the result of such prior attempts to solve the production of reliable subsonic cartridges have failed and let to subsonic rounds that have a larger variation in velocity and variance in accuracy potential.
In addition the use of polymer ammunition results in additional drawbacks, e.g., the possibility of the projectile being pushed into the cartridge casing, the bullet pull being too light such that the bullet can fall out, the bullet pull being too insufficient to create sufficient chamber pressure, the bullet pull not being uniform from round to round, and portions of the cartridge casing breaking off upon firing causing the weapon to jam or damage or danger when subsequent rounds are fired or when the casing portions themselves become projectiles. Accordingly, a need exists to develop solutions that make it possible to manufacture better and more price competitive subsonic ammunition than previously available.